A more precise instrument than the general concept of ego strength is needed in the study of ego deviation and schizophrenia. Such an instrument is the detailed analysis of the separate ego functions. This paper makes the specific ego functions, their development in childhood, the resultant ego deviations and the relation to the concept of schizophrenia the focus of consideration. The interrelationship of functions in an approach to the human psyche as a unit, however, is not overlooked. Sections are devoted to the relation to reality, regulation, and control of instinctual drives, object relations, thought processes, defence functions of the ego, autonomous ego functions, and the synthetic function. A good deal of case material illustrating ego disturbances in children who